Key concepts
Physics
Engineering
Civil engineering
Water

Introduction
Irrigation, the artificial application of water to crops, has been used by humans for thousands of years. Ancient civilizations built complex irrigation systems without the aid of modern technology or construction equipment. Can you design a model irrigation system using simple household materials? Try this project to find out!

Background
Irrigation systems can be vital for growing crops in areas that do not otherwise receive enough rainfall to sustain them. They are even used in areas that are near natural water sources such as lakes and rivers to help evenly distribute water among crops. Modern irrigation systems can rely on heavy construction equipment to dig miles of trenches and pumps that can suck water up from deep underground. Electrical power allows us to distribute water through miles of piping across farm fields.

How did ancient civilizations manage to build irrigation systems thousands of years ago? They took many different approaches. For example, they could divert the natural flow of a river toward their crops, use lakes as reservoirs to store extra water for dry seasons or rely on gravity-powered systems to channel rainwater coming down a mountainside. In this project you will build a simple model irrigation system using plastic cups and straws powered by nothing but gravity. Can you design a system that evenly distributes water among different cups, simulating how a real irrigation system would send equal amounts of water to different fields?

Materials

• Paper or plastic cups (at least four; they can be different sizes)
• Drinking straws
• Modeling clay
• Scissors
• Utility or craft knife
• Tap water
• Work area where it's OK to spill water, such as a sink, bathtub, large plastic tub or an outdoor area
• Towels if working indoors to clean up any spilled water
• Coins to help weigh the cups down (optional)

Preparation

• Have your adult helper use the knife to make two small X-shaped slits about one-third of the way down from the top of a cup, on opposite sides of the cup.
• Get two more cups and make one X-shaped slit in each up, about one-third-of the way up from the bottom, but slightly lower than the slits in the first cup (the slits in the first cup should be higher than the slits in the second two cups). Why do you think it is important to have the holes at different heights?

Procedure

• Poke one drinking straw through each slit in the first cup. Then poke the other ends of the straws through the slits in the other cups.
• Use small pieces of modeling clay to form a seal around the straws inside each cup to prevent water from leaking out around it.
• If you have trouble getting the cups to sit flat, put a few coins in the bottom of each one to help weigh them down.
• Slowly pour water into the central cup. What do you think will happen? You can pretend this central cup represents a natural water source, such as a river or lake, or an area that receives rainfall. Pretend that the other cups represent locations without water. What happens when the water reaches the straws? Why?
• Extra: Make this project an engineering design challenge. The instructions only tell you how to build a very simple model irrigation system, but this should be enough to get you started. Here are some additional challenges you can try. Feel free to try using other materials that are not listed in the materials section above.
• Can you design a bigger irrigation system with more cups that all receive water from the central cup? Can you make sure that they all receive the same amount of water when you pour water into the central cup?
• Can you design a "chained" irrigation system, where water passes from one cup to the next? Is it possible to get the same amount of water in each up? What challenges do you encounter in designing and building this system?
• Can you transport water over a longer distance? Can you figure out how to space the cups farther apart than one straw length?
• Extra: There are also some scientific tests you can do based on this project. What happens if you change the angles of the straws, making them steeper or shallower? Does this change how much water each cup receives? What if you change how fast you pour the water (e.g. pour the water so fast that the first cup fills up before it has time to drain through the straws, vs pouring the water slowly so it drains through the straws right away)?

Observations and results
When you pour water into the central cup, it should start flowing into the other cups once it reaches the straws. This occurs because gravity pulls the water through the straws, which are angled downward—because you made the holes in the first cup higher than the holes in the other cups. To get equal amounts of water in each cup, it is important to have the straws in the central cup all at the same height. If one straw is higher than another, the cup it leads to will not receive as much water (or any water at all, depending on how slowly you pour the water—if you pour slowly enough, all of the water might go through the lower straw).

You might experience some leaks through the modeling clay seals, which is why it's a good idea to do this project where it's OK to spill some water!

This activity was inspired by: Way to Flow—Water Irrigation, by eGFI.

More to explore
Irrigation, from National Geographic Society
Clean Dirty Water with the Sun, from Scientific American
Science Activities for All Ages!, from Science Buddies

This activity brought to you in partnership with Science Buddies